The present invention relates to a homogeneous charge compression ignition internal combustion engine (HCCI internal combustion engine) that performs EGR for recirculating exhaust gas to a combustion chamber. Also, the present invention pertains to a method for controlling ignition timing of premixture in an HCCI internal combustion engine.
For example, Japanese Laid-Open Patent Publication No. 2000-64863 discloses an HCCI internal combustion engine that performs EGR. In this publication, when compression ignition is performed with a low load, closing timing of the exhaust valve is advanced to a point in exhaust stroke immediately before the piston reaches the top dead center. That is, the closing timing of the exhaust valve is advanced to a point before the piston reaches the top dead center in the exhaust stroke. Accordingly, high temperature combusted gas stays in the combustion chamber as internal EGR gas. The internal EGR gas is mixed with new air drawn into the combustion chamber in the subsequent cycle. This improves the ignitability of compression ignition. Also, the apparatus of the publication performs compression ignition when the load is low and performs spark ignition combustion.
Typically, in an HCCI internal combustion engine, fuel and air is premixed and the mixture is compressed to self-ignite. Control factors including the temperature, the pressure, and the fuel concentration must be appropriately controlled such that self-ignition occurs when the piston is at the top dead center or in the vicinity thereof. The control of these factors is extremely difficult. Accordingly, such an engine is operated in a region where the control of the factors is not difficult. As a result, the operational region is narrow.
The operational range of the HCCI internal combustion engine of the above publication is desired to be widened so that compression ignition can be executed in a range where spark ignition is currently executed. This will maximize the advantages of compression ignition, or a high thermal efficiency and less emission of toxic substances.